In a typical electrophotographic imaging apparatus, such as a printer, copier, plain-paper facsimile machine, etc., a series of rollers are generally used in order to permanently affix an image once photographic toner has been applied to the paper or other recording medium. These rollers will usually be configured so that at least two rollers will be in contact with each other and will be rotatable in opposite directions, and the paper receiving the photographic image will be directed to pass between these two rollers. In this type of arrangement, one or both of the rollers will be designed to apply heat in order to permanently fix the image on the paper, and this fixing step will be further aided by having at least one of these rollers made of a resilient material so that it will apply a sufficiently high pressure to the paper simultaneously with the heat. In this configuration, the roller applying the heat to the recording medium is generally known as a "fuser roller", and the resilient roller applying pressure to the paper is thus referred to as the "pressure roller."
In these electrophotographic heated imaging devices, it is thus necessary to apply sufficient heat and pressure to ensure that the photographic toner is permanently affixed to the paper in order to produce the final image. However, because of these extreme heat and pressure conditions, there is also a great tendency for the paper to stick to the heated fuser roller during the copying process, and this tendency to stick must be overcome in order to ensure the proper functioning of the heated imaging device.
In general, to overcome the problem of sticking to the fuser roller, these heated imaging devices typically will use a release agent such as silicone oil which is applied to the surface of the fuser roller in a manner which eliminates or reduces the tendency of the paper to stick during the fusing step. At present, there are many products used in the industry to supply the oil to the fuser roller. Higher quality printing and color printing has driven a need for consistency in the oil laydown. Previous designs of oil supply sources were temperature-tolerant felt pads (often made from aramid fibers), rollers with metal cores wrapped with aramid felts and oiled, oiled ceramic core rollers wrapped with aramid felt, and metal core tank rollers with holes that allowed oil to flow to the aramid felt wrap.
Unfortunately, none of these prior art devices are suitable for providing a consistent and even distribution of release oil onto the surface of a fuser roller. For example, the problem with devices featuring a felt-wrapped oil supply source is their inconsistency. As the oil is applied to the fuser roller, the fibers of the felt often cause a streak pattern on the final image. This pattern can be seen on the printed page with a black light if a UV tracer is added to the oil when the supply device is fabricated. Thus, the amount of oil that flows out of these types of oil supply devices is also relatively uncontrolled. As the oil supply device comes in contact with the hot fuser, the viscosity of the oil is reduced and the oil flows onto the fuser unabated.
Another problem inherent in these prior art oil supply devices is what is referred to as oil "dumping." This condition refers to the large amount of oil transferred to the first few pages as the copier or printer is started. This happens because the oil supply source is in contact with the hot fuser while the machine is idle, and a pool of oil gets deposited. While the fuser is running a large batch job, the oil laydown may eventually improve in consistency, but this occurs at the sacrifice of the initial startup pages.
Even further, as machines increase print and copy resolution, and as color copies and prints become more common, a consistent source of release oil supply is imperative. These higher performance levels require a consistent oil laydown with no streaking or dumping. In the case of color, the oil laydown can affect the color consistency of the printed page and is a particular concern with transparencies.
In the patent arts, there have been many devices that have been disclosed for applying a release oil to the fixing roller of a copying or printing apparatus. These patent references include U.S. Pat. Nos. 5,534,062; 5,478,423; 5,709,423; 5,232,499; 5,594,540; 4,668,537; 4,309,957; 4,908,670; 5,267,004; 3,831,553; and 3,718,116. In addition, such devices are disclosed in foreign patent references Eur. Pat. App. 479,664 and Japanese Laid-Open Patent No. 62-178992. In some of these patent references, devices have been disclosed which attempt to provide a suitable oil control layer made of materials such as polytetrafluoroethylene (PTFE), such as in Eur. Pat. App. 479,564, but these layers are used in conjunction with an open-celled foam interior which has an extremely limited oil capacity and which is extremely difficult to recycle or refill. Similarly, Japanese Patent reference no. 62-178992 discloses a device which consists of an oil permeation layer adhered to a thick porous material which serves as a wick or reservoir for supplying oil to the permeation control layer. Once again, the reservoir capacity of such devices are extremely limited, and in addition, have extremely limited lifetimes because of the deformation and failure of the thick porous material supporting the permeation control layer which limits performance and requires frequent replacement.
Accordingly, there is thus a substantial need in this field to develop a method and apparatus for applying a release oil to a fusing roller in a printer or copier which has a sufficiently large oil capacity, which can be simply and efficiently operated for an extended period of time, and which can ultimately safely and easily be recycled and/or refilled. There is also a substantial need to provide a means whereby a release oil can be applied to a fuser roller in such a manner as to obtain a consistent oil laydown with little or no streaking or dumping. Finally, there is a substantial need to provide a means for achieving an even distribution of oil onto a fuser roller in a printer or copier which avoids the many other problems associated with the prior art devices in this field.